1. Field of the Invention
The present invention relates to piping systems for conducting mixed flows of gas and particles, and more particularly to coal piping systems.
2. Description of Related Art
A variety of devices and methods are known in the art for delivering pulverized coal to coal fired burners. Of such devices, many are directed to improving particle distribution within coal piping systems for delivering coal to be combusted.
Coal powered plants require an efficient means of supplying coal as fuel to produce heat power. Raw coal is typically pulverized in a coal pulverizer or mill to produce small coal particles or coal dust. The pulverized coal must then be delivered to a furnace or burner where it can be used for combustion. This is typically done with a coal piping system that utilizes air flows to transport pulverized coal particles from the mill or pulverizer to a nozzle where coal particles are injected into the coal burner or furnace. As the coal particles travel in the air flow through the piping system, bends in the piping and the pipe geometry in general tend to cause non-uniform coal particle distribution. This non-uniform distribution frequently occurs just downstream of elbows in a piping system.
Non-uniform particle distribution causes various technical problems for operation and maintenance of coal systems. If poor particle distribution extends into the combustion zone, localized imbalances in the fuel/air mixture can cause inefficient combustion and elevated emissions of NOX, CO, and other pollutants. It can also cause elevated levels of unburned carbon in the fly ash, which will lower combustion efficiency. The highly abrasive nature of the coal rope impacting and scrubbing components of the coal piping and burning system causes extensive erosion of pipes and other components in the system, leading to frequent need for inspection, repairs, and replacement of parts. If inspections, repairs and replacements are not performed in a timely manner, there is an elevated chance that abrasion from coal roping will cause expensive or dangerous failures of key components. Poorly distributed particles can also hamper the performance of components like the classifier. For example, an uneven particle distribution flowing into a coal classifier can cause one portion of the classifier to wear out earlier than the rest and can lead to full utilization of only a portion of the classifier.
Various solutions to the problem of particle distribution in coal piping systems are known in the art. Known systems are designed to break up coal ropes, which are concentrated regions of coal particles running through a piping system. The known systems are generally used to break up coal ropes just upstream of coal nozzles/burners to provide an even distribution of particles into the combustion zone.
Such conventional methods and systems generally have been considered satisfactory for their intended purpose. However, there still remains a continued need in the art for methods and devices that can improve particle distribution upstream of components other than the burners. There also remains a need in the art for such methods and devices that are easy to install and/or replace and that impart low pressure drop. The present invention provides a solution for these problems.